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tns1 09-10-2009 01:18 PM

Panel ground and wire size
 
I am replacing my service entrance panel (meter breaker). The earth ground on the existing panel is a #6 alum wire which runs about 15ft to a copper water supply pipe. The connection is about 8ft from where the pipe first enters the home.

The NEC has page after page on grounding and it isn't easy to follow.
As far as I can tell, this wire is called the 'grounding electrode conductor'.

250.52 states, "Interior metal water piping located
more than 1.52 m (5 ft) from the point of entrance to the
building shall not be used as a part of the grounding
electrode system
..." If the 'point of entrance' refers to the electrical service, then 15ft is too far. If it means water service, then I can move the clamp a few feet and it will comply.

When would a water pipe NOT be sufficient as a ground? In other words when would I have to put in a ground rod?

Table 2.52 shows that the gauge of this wire is loosely based on gauge of the service entrance wire. My #6 would be OK as long as the service wires were #2 or smaller. I'll have to find out what they plan to install for a 200amp service.

HouseHelper 09-10-2009 02:05 PM

The #6 (or#4) COPPER grounding electrode conductor (that's right, it must be copper) should connect within the first 5 ft of the water line entry AND a supplemental electrode (ground rod) must be used in addition to the water line.

tns1 09-10-2009 03:28 PM

OK, I see that in 250.53(D)(2). So two different types of ground are required.

I sure wish I knew that when I dug my service trench. I could have laid a ground bar down in the trench. Other ground electrode options (ring, plate) would also have been easy.

Is the supplemental electrode requirement something recent? It must not have existed when my house was built 30+ years ago.

Actually, I did notice that just below my meter, at the edge of the slab, I can see the very end of a piece of horizontal rebar. This rebar is, I assume, completely encapsulated in the slab (I can only just see the end). I had assumed this was just sloppy work, but now I wonder if it was intended to be a ground electrode.

tns1 09-10-2009 06:31 PM

Well, that rebar would not be a very good ground since the measured resistance to my pipe ground is way too high.

The city says use #4 copper for all ground electrode conductors, and to add a ground rod (or plate, ring). What do you use to pound an 8ft rod into very hard ground? Since I have already trenched 4ft deep there, I only worry about the last 4ft, but I sure don't want to get to the last foot and find it won't go further. How much pounding can these take without bending?

wirenut1110 09-10-2009 07:31 PM

It's #4 for your cold water pipe, but for your supplementary electrode is not required to be larger than #6 copper.

I use my hammer drill to drive rods, some use slide hammers and some use a sledge.

tns1 09-10-2009 07:49 PM

So have you ever had to pull one out and put it in at an angle because the ground was too hard?

wirenut1110 09-10-2009 08:04 PM

No but, our area isn't that rocky. Have had quite a few difficult ones but, none that didn't eventually give in. If it's hard in a spot, I just pull it up and try another area a foot away or so.

Just whatever you do, don't cut it off and take a hammer and flare the top so you can't tell you cut it off.:whistling2: Put your clamps on first too, cause once the rod flares out, it won't go on.

tns1 09-10-2009 08:31 PM

Quote:

Originally Posted by wirenut1110 (Post 326271)
Just whatever you do, don't cut it off and take a hammer and flare the top so you can't tell you cut it off.:whistling2:

Very tempting I am sure. If it ohmed out less than 25ohms would the inspector know or care? He'd have to use a reflectometer to know if it was short.

Scuba_Dave 09-10-2009 08:48 PM

Also make sure you put that (acorn) nut on before you use a sledge hammer to drive it in
I had one that was tough to drive in, kept the hose running on a trickle for a while
Helped a lot

tns1 09-10-2009 09:43 PM

I see in 250.64(B), the ground electrode conductor must be protected "where exposed to physical damage". If its inside the wall or underground, it isn't exposed to damage, but I'll have a very short 6" section running down the side of the slab which is exposed. I am guessing that needs to go in a short length of pvc, although I looked at a recent job that simply ran the insulated ground wire down the exterior siding into the ground.

If I read this section right, a smaller (thinner, weaker) conductor is somehow deemed to be less subject to damage than a larger one?

Scuba_Dave 09-10-2009 09:47 PM

I put my #4 in conduit about 10-16" into the ground
Not sure how much now
That stick of conduit is a lot less $$ then replacing the wire :yes:

AndrewF 09-10-2009 09:59 PM

I just put 4 rods in.

2 for the house, and I used a hammer drill.

The other two were for my barn. I only used a hammer for the last 2'. I put the rod in about 6", pull it out, put water in, and repeat.

Yes, remember to put the clamp on BEFORE you start hammering it, otherwise the top is likely to get mangled and you wont get the clamp on.

tns1 09-10-2009 10:02 PM

I did not see anything about how deep the top of the rod (or conductor) needed to be to be considered 'protected'.

tns1 09-10-2009 10:08 PM

Quote:

Originally Posted by Scuba_Dave (Post 326293)
I had one that was tough to drive in, kept the hose running on a trickle for a while

A great idea.

SD515 09-11-2009 07:01 AM

Quote:

Originally Posted by tns1 (Post 326329)
I did not see anything about how deep the top of the rod (or conductor) needed to be to be considered 'protected'.

The way the inspectors in my area interpret the code is that the code says that 8 feet (of a 5/8" copper rod [most common here], 10 ft of galv rod) has to be in contact with the earth. Since the rod is 8 feet long (or 10), the top of the rod has to be at ground level, or slightly below. I put 'em about 1 or 2 inches below ground level, but leave it dug out some for the inspector to see the 'acorn' connection, bury it afterwards. I bury the wire from the rod to the building, and usually don't need to use conduit at the bldg if the exposed wire is a short run...usually 6" or less.


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